    [Prior-Art 1] U.S. Pat. No. 6,693,912B1, “Network Interconnectivity Apparatus and Active Quality of Service Mapping Method,” February 2004.    [Prior-Art 2] US 2004/000 1511 A1, “Catprobe,” June 2002.    [Prior-Art 3] US 2004/009 5912 A1, “Handover Resource Optimization,” November 2002.
The increasing popularity of mobile wireless communications has resulted in the development of numerous communications technologies. Each technology addresses user needs in different environments, under different circumstances or during different time periods. Consequently, the entirety of user needs is addressed by a combination of different technologies. So users will utilize heterogeneous communications networks to satisfy their needs.
Among the numerous technologies, is the IEEE 802.11 wireless local area network (WLAN). This communications technology is used in localized areas of high communications activity or hotspots. They are generally available at locations such as residences, offices and shops. IEEE 802.11 WLANs are characterized by gross achievable data rates of 11 Mbps or 54 Mbps. This is the data rate available at the physical layer. The typical sustained throughput as calculated at the IP layer is approximately 4 Mbps to 5 Mbps and 10 Mbps to 20 Mbps, respectively, due to header, signaling and timing overheads. Due to its contention-based CSMA/CA radio access technique, IEEE 802.11 WLANs are also characterized by high packet loss-rates and long radio access delays. The performance of IEEE 802.11 WLANs is also affected by their locations. For example, IEEE 802.11 WLANs located in an office environment are utilized by more users than those in a residential environment. As a result, the load levels and consequently, delays are higher for office IEEE 802.11 WLANs.
Another technology that addresses user needs is the cellular GPRS network. This communications technology has been used to cover large areas of many square kilometers. Cellular GPRS networks are characterized by gross achievable data rates of 171 Kbps. Due to its contention-free TDMA radio allocation technique, cellular GRPS networks are characterized lower packet loss-rates and shorter radio access delays as compared to IEEE 802.11 WLANs.
Another communications technology that is currently being increasingly deployed is cellular third-generation (3G) networks. This technology is used to cover large areas similar to those of cellular GRPS networks. Cellular 3G networks are characterized by gross achievable data rates of 384 Kbps with further developments in process of delivering even greater data rates. Due to its radio allocation technique in which unique codes are used for radio access, contention is avoided. This leads to lower packet loss-rates compared to IEEE 802.11 WLANs. Given its nascent state, cellular 3G networks are not as widely available as cellular GPRS networks.
In general, communications network technologies are characterized by differences in achievable data rates or throughput, packet loss-rate, retransmission delay, retransmission attempts, radio access delay and network load conditions. The resulting heterogeneity requires innovative methods for effective operation.
Mobile wireless user terminals typically use a combination of different communications technologies to meet their needs. For example, a mobile wireless user terminal will use a multi-mode terminal device to access an IEEE 802.11 WLAN while at home, then switch to a cellular GPRS network when driving from home to the city, then switch again to a cellular 3G network when entering the coverage area in the city downtown area and finally switch back to an IEEE 802.11 WLAN when reaching the office.
[Problem 1: Sudden Switching Disrupts Performance]
So as mobile wireless user terminals switch between technologies of different communications networks, their varying characteristics and conditions alter the quality of service (QoS) performance for the users and their applications. For example, when switching from an office IEEE 802.11 WLAN to a cellular 3G network, users encounter lower throughput and simultaneously, reduced packet loss-rates and shorter radio access delays. So, if the user was using a streaming video application, there will be an abrupt disruption or degradation of video quality after the network switch. Application performance must be preferably seamless when switching from one type of network technology to another. Alternatively, application performance must be gradually adapted to prevailing network conditions and characteristics.
The transition period between one communications network to another is a critical part of communications. It is during this period that mobile wireless user terminals and their applications are most vulnerable to disruption. This is seen by the fact that in traditional, non-heterogeneous communications networks, service providers assign greater priorities to transitioning sessions as compared to newly originating sessions.
[Problem 2: QoS Mapping Adds Overhead and Time]
Furthermore, due to the changes in link characteristics resulting from switching between communications networks, mobile terminal devices must map their existing QoS requirements to the new link characteristics and conditions. This is an intensive and time-consuming task for mobile terminal devices, which have limited battery power. When a user switches frequently, mapping of QoS requirements becomes a processing overhead that adversely affects QoS performance. Additionally, signaling required for negotiating QoS resources at new communications networks is also time-consuming because greater exchanges are required to confirm and establish appropriate QoS requirements, which are not known to the mobile terminal device.
[Problem 3: Inefficient Resource Utilization]
Another problem arising from switching between technologies of different communications networks is that QoS resources are not efficiently allocated due to differences in mobility conditions. For example, when two users switch to an IEEE 802.11 WLAN—a first user from a cellular 3G network and a second user from another IEEE 802.11 WLAN—both will make identical QoS resource requests to the new IEEE 802.11 WLAN. However the first user from the cellular 3G network will have substantially lower actual throughput requirements due to the user's past history with the lower-throughput cellular 3G network. So allocating identical QoS resources to both requests is inefficient as the first user from the cellular 3G will not completely utilize them. This problem is exacerbated when there are large numbers of users moving to an IEEE 802.11 WLAN from different types of previous communications networks.
[Problem 4: Unauthenticated QoS Requests]
Related to the problem of inefficient resource allocation, is the problem of inaccurate QoS resource requests. Based on extant technologies and prior arts, it is not possible for a communications network to verify the exact nature of a user's QoS resource request. As a result, a communications network must allocate the entirety of request QoS resources even if the user utilized substantially lower resources at a previous communications network. For example, when a user switches from a first to a second communications network, it is not possible to verify which type of network the user switched from, the level of resource utilization at the first network and the time duration spent at the first network. As a result, the second communications network cannot allocate the optimal level of QoS resources. So inaccurate resource requests, whether legitimate or illegitimate, cannot be verified by technologies of existing communications networks.
Such problems of abrupt performance changes, switching overhead, inefficient QoS resource allocations and unauthenticated QoS requests deprives mobile wireless user terminals of seamless communications. Consequently, mobile wireless user terminals suffer from poor QoS performance.
[Prior-Art 1] illustrates a method for adjusting QoS performance when a mobile wireless user terminal switches from one communications network to another. The method relies on an active packet—indicating QoS characteristics of the first communications network—being sent to the second communications network. The method, despite its theoretical basis, has limited practical appeal because it requires the two different networks to be in communications with each other. In reality, communications networks of different technologies are not communicably coupled. This is because of security concerns, competitive advantage and incompatibility. So the proposed method is not effective in solving the needs of mobile wireless user terminals.
[Prior-Art 2] presents a method for a first communications network to determine the QoS conditions at a second communications network by means of ICMP time-stamp messages. This method is disadvantaged similarly to [Prior-Art 1] in that it requires the two networks to be communicably coupled in order to be effective. So in practice, this method is not a feasible solution to address the problems faced by mobile wireless user terminals that switch between different communications networks.
[Prior-Art 3] illustrates yet another method to address the needs of mobile wireless user terminals switching between communications networks. This method utilizes foreign agents at each communications network and requires them to collaborate to provide consistent QoS across handovers. This is not feasible for the practical cases in which mobile wireless user terminals switch between distinct communications networks that do not offer a medium for coordination. The foreign agents of this method are not effective in addressing the problems highlighted earlier.
The prior arts discussed insofar illustrate the lack of existing mechanisms to address the needs of mobile wireless user terminals that switch between distinct communications networks. In particular, these users are faced with the problems of abrupt performance changes, switching overhead, inefficient QoS resource allocations and unauthenticated QoS requests, which consequently deprive them of seamless communications.